1. Field of the Invention
This invention pertains generally to high voltage structures or devices including structures or devices for storing or transmitting electrical energy, and more particularly to reducing electric fields at the edges of conductors on insulators in these high voltage structures or devices.
2. Description of Related Art
When an insulator is placed between two conductors, typically metal, and the conductors are energized with high voltage, the electric field in the insulator reaches a maximum at the edges of the conductors. This enhanced field causes the insulator to fail at significantly lower electric potentials than it would without such field enhancement. The problem becomes more serious as the thickness of the conductors decreases, setting a limit on the electric field gradients that can be achieved, with a resulting limit on the ability to build compact high voltage systems.
The field enhancement is internal to the insulator material itself. A failure of the material would result in an internal bulk breakdown of the material. The cause of the field enhancement is the sharp edge of the conductor. The potential around this sharp edge discontinuity changes very rapidly by comparison to other regions away from the edge so the net result is an increased electric field. Breakdowns of this type occur very rapidly.
Various structures or devices for storing or transmitting electrical energy, e.g. capacitors, transmission lines, and accelerator components (e.g. Blumlein pulse generators), are constructed with pairs of conductors separated by insulators. These conductors generally form electrodes or transmission lines. For high voltages to be placed on these electrodes or transmission lines, the underlying insulator must not break down. The higher fields produced at the edges of the conductors decrease the voltage that can be placed across the conductors before breakdown occurs.
To make the structures or devices compact, the components, both conductors and insulators, must generally be made as thin as possible, requiring high gradients across the insulators. This magnifies the problem created by the field enhancement at the conductor edges.
Prior approaches to deal with the problem have generally focused on geometrical solutions. These have included rounding the edges of the conductors and using multiple dielectrics. However, these techniques have not been totally effective in combating the enhanced edge fields.